Foamed polymeric materials have found use in many industrial applications. Foams are generally made of either thermoplastic or thermoset materials. Polyurethane foams comprise the most widely-known thermosetting polymer foams. Typically, thermoset foams are cured as foam formation occurs, and no post-foaming cure is possible or necessary. The largest industrial volumes of thermoplastic polymer foams include polystyrene and polyethylene foam.
Foamed structures have been prepared using both chemical and physical blowing agents. Chemical blowing agents are materials that decompose, typically upon heating, to produce a gas. The formation of gas bubbles within a polymer matrix produces a polymer foam. Physical blowing agents are materials that are typically gases at ambient temperature and pressure, which are mixed with a polymer to form a foam. Physical blowing agents are typically used in a foaming process in a liquid or supercritical form under high pressure. Liquid or supercritical carbon dioxide is an example of a physical blowing agent. Upon an increase in temperature or reduction in pressure, the blowing agent expands, producing foam in the polymer matrix in which it is mixed.
Foam tapes comprise an important industrial segment. Typical constructions include a foam layer that may have a backing layer and, on an opposite side, an adhesive layer, such as a pressure-sensitive adhesive layer. Alternatively, an adhesive layer may be coated on both sides of a foam layer to make, e.g., a mounting tape. Such a tape may be stiff or compliant, thick or thin, depending on the nature of the foam.